use Time::Local qw( timelocal );
use strict;
my @input = reverse qw(
	Order_29May11:05.bak
	Order_11Jun20:25.bak
	Order_10Jun14:16.bak
	Order_10Jun16:04.bak
); # reversed to prove it works since they are already sorted
my @months = qw( Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec );
my %months;
for (0 .. $#months) {$months{$months[$_]} = $_}
# merlyn's definition of the
# Schwartzian Transform
# changed to numerical sort 

my @output =
  map { $_->[0] }
  sort { $a->[1] <=> $b->[1] }  
  map { [$_, expensive_func($_)] }
  @input;

print join "\n", @output;
exit;
sub expensive_func { 
	# convert filename to date
	$_[0] =~ /Order_(\d+)(...)(\d+):(\d+)\.bak/ 
		or die "bad filename $_[0]";
	return timelocal(0, $4, $3, $1, $months{$2}, 0);
}

__OUTPUT___

Order_29May11:05.bak
Order_10Jun14:16.bak
Order_10Jun16:04.bak
Order_11Jun20:25.bak